1. Field of the Invention
This invention relates to the art of preparing micron size particles of solid polymeric materials having narrow particle size distributions.
2. Prior Art
In many applications where polymeric materials are employed, it is advantageous to have the polymer in a narrow distribution of relatively small particles and particularly in the micron range, i.e., 0.1-10 microns. This is particularly the case when the intended use of the polymer is as a coating or adhesive material to be applied in the solid state, e.g., as by dispersion. For example, U.S. Pat. No. 3,616,047 discloses that when dispersions of polypropylene and carboxylated polypropylene are used as an adhesion promoting coating for bonding polypropylene closure members to enamel coated metal surfaces, improved adhesion results if the dispersed polymers have a particle size of less than 5 microns.
Although polymer particles of micron size of narrow distribution are desired by the art, small, uniformly sized particles are difficult to obtain. For example, the most convenient way of obtaining polypropylene particles of micron size is by direct polymerization. However, direct polymerization techniques have not been consistent in producing micron size polypropylene particles. Grinding of flake polypropylene has been tried but with very limited success as the procedure produces a broad distribution of particle sizes and the high cost of energy required to achieve the micron particle size places the product out of commercial consideration.